Many modern engines use variable geometry turbines (VGT) as part of turbocharger systems for refined engine control, transient response, and lower emissions. A function of a VGT depends on a position of internal vanes that direct a flow of exhaust gas to a turbine wheel. These internal vanes are also capable of modulating a pressure drop across the VGT, effectively controlling a pressure of the exhaust gas upstream of the VGT. Control of exhaust pressure in an engine is advantageous to engines having exhaust gas recirculation systems, because a pressure difference between an intake system and the exhaust system may be controlled to augment the flow of exhaust gas to be recirculated.
Current VGT designs use complicated and costly internal vane assemblies that have many moving parts. This often leads to use of exotic materials and/or precise manufacturing methods to improve the function and reliability of VGTs.
Accordingly, there is a need for providing a system which utilizes a simple, free-flow type turbocharger, that is less expensive and complicated than a VGT, but that still provides control of exhaust manifold pressure and engine intake manifold boost.